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Explain Minimum mode of 8086 microprocessor. Draw timing diagram for write operation in minimum mode and explain it.
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  • 8086 works in Minimum Mode, when MN/ ¯MX = 1.
  • Minimum Mode, 8086 is the only processor in the system. The Minimum Mode circuit of 8086 is as shown below:
  • Clock is provided by the 8284 clock generator, it provides CLK, RESET and READY input to 8086.
  • Address from the address bus is latched into 8282 8-bit latch. Three such latches are needed, as address bus is 20-bit. The ALE of 8086 is connected to STB of the latch. The ALE for this latch is given by 8086 itself.
  • The data bus is driven through 8286 8-bit trans-receiver. Two such trans-receivers are needed, as the data bus is 16-bit. The trans-receivers are enabled through the DEN signal, while the direction of data is controlled by the DT/ ¯R signal. ¯DEN is connected to ¯OE and DT/ ¯R is connected to T. Both ¯DEN and DT/ ¯R are given by 8086 itself.

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  • Control signals for all operations are generated by decoding M/¯IO , ¯RD and ¯WR signals.

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  • M/¯IO , ¯RD and ¯WR are decoded by a 3:8 decoder like IC 74138. Bus Request (DMA) is done using the HOLD and HLDA signals.
  • ¯INTA is given by 8086, in response to an interrupt on INTR line.

Minimum Mode configuration of 8086

Minimum Mode Write Cycle

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